Optical networks continue to grow at a high rate, driven by the increase in the size of the Internet. As they grow their energy consumption increases, so that the combined energy consumption of the data network has become a significant fraction of the total energy consumption of a country. For example, Telecom Italia's network consumed over 2 TWh in 2005, which is approximately 1% of the total Italian energy demand. It is therefore important to find methods to reduce the energy consumption of optical networks.
Optical networks are not fully planned and constructed at one time, but have a tendency to grow by adding new links to increase capacity, with minimal modification to the current links in order to minimize disruption. It is known that in the Optical Transport Network (OTN) larger Optical Data Units (ODUs) can be transported and switched using much lower energy than smaller ODUs. Therefore, optical links with large amounts of traffic consume less energy per bit than links with a smaller amount of traffic. This means that over time the energy efficiency of the optical network will move away from an optimum, even if the original design had close-to-optimum energy consumption.
It is possible to reduce the energy consumption of the network by changing the network topology, either in part or in total, as links are added or removed. However, this would be costly because it would involve changing network equipment, and disruptive because network operation would be interrupted. In most cases it is important to minimize the disruption in the traffic by only changing links that have the most significant impact to energy consumption. We teach a method to reduce network energy consumption with a minimal amount of traffic redistribution.